Calcitonin gene-related peptide (CGRP) and the regulation of cerebral parenchymal vessels.

The role of calcitonin gene-related peptide (CGRP) in the cerebral microcirculation was examined in fourteen anesthetized cats. The local cerebral blood volume (CBV) and blood flow (CBF) in the temporoparietal cortex were measured by our photoelectric method. CBV represents the cumulative dimensions of the parenchymal vascular network. Intracarotid injection of 0.1, 1, and 10 micrograms/kg CGRP8-37, a CGRP antagonist, had no significant effects on CBV and mean arterial blood pressure (MABP). Intracarotid injection of 0.1 and 1 microgram/kg CGRP, but not 0.01 microgram/kg CGRP, increased CBV in a dose-dependent manner (P < 0.05). CBV was initially reduced following 1 microgram/kg CGRP injection, possibly reflecting the marked fall in MABP (P < 0.01) with this dose. Following injection of 0.1 and 1 microgram/kg CGRP, CBF was also increased by +7.3 +/- 7.7 (+10.7%) and +13.1 +/- 4.8 ml/100 g brain/min (+20.4%, P < 0.05) at 15 min. The CBV increase elicited by 1 micrograms/kg CGRP was inhibited (P < 0.05) by preinjection of 10 micrograms/kg CGRP8-37. It is concluded that CGRP has no significant role in the maintenance of resting tone of intracerebral microvessels. However, circulating CGRP dilates the small parenchymal vessels through a specific CGRP receptor, and thereby is involved in the evolution of pathologic conditions.